Multireflex resnatron



M. GARBUNY MULTIREFLEX RESNATRON March 12, 1957 Filed oct. l26.` 1951 2 She'ets-Sheet 1 March l2, 1957 M. GARBUNY MULTIREFLEX REsNATRoN 2 Sheets-Sheet. 2

Filed Oct. 26. -1951 wim-11P- l INVENTOR NWA GHZBl//V Y S Z BY z ATTORNEY 2,785,334 Patented Mar. i2, i957 MULTIREFLEX RESNATRON Max Garbuny, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 26, 1951, Serial No. 253,252

7 Claims. (Cl. S15-5.18)

This invention relates broadly to an eiectronic tube for ultra high frequencies, and has particular relation to a device of that character generally identied as a resnatron and which is, according to the following disclosure, a multireliex resnatron.

Ultra high frequency electron tubes of the cavity resonator type are, notwithstanding their capabilities of power and efficiency, inherently limited in band width. This limitation arises quite generally from the fact that the electron beam when crossing the cavity gap interacts only a short time with the electromagnetic field. An efiicient interchange from kinetic into radio frequency energy, or vice Versa, presupposes therefore that the radio frequency vol*- age over the gap, and consequently also the loaded shunt resist-ance and Q are high enough. For instance, the shunt resistance in resnatrons has to have -a value suiciently high so that at a given power. level the developed radio frequency voltages match the energy of the beam. It might appear that, for the sake of example, lowering of the anode voltage while increasing the current, might combine the advantages of low impedance with high efficiency; how* ever, a high current can be gained only at the price of high grid voltages, and Vthus the gain would be sharply reduced with such procedure.

The increasing demand for wide band amplifiers, on the other hand, has led to the development of tubes in which the interaction between eld and beam extends over many cycles so thatV the loaded shunt resistance is allowedto be small and the bandwidth high. These devices, of which the most outstanding representative is the travelling wave tube, sutfer inherently, however, from stringent limitations in power and efiiciency.

According to the present invention, it is proposed to combine the advantages of cavity gap interaction, with its resulting possibilities of efiiciency and power, with those of a low shunt resistance obtainable through repeated energy exchange in small steps and through extension of time vduring which the electrons continue in energy-exchanging transit.

More specifically, anl object `of the invention is to send a density modulated electron beam repeatedly through the same resonator gap. v

A further objective is to provide'a multireex resnatron having greater bandwidth than theretofore obtainable in resnatrons.

Another object of the invention is to obtain, with all stages of reflection, return or reflection of the electron over a path ,other than the path of approach.

The invention has an objective of providing a device cap-able of producing the desired effects and fulfilling the requirements of resonance and static field conditions necessary therefor.

Furthermore, an object ofthe invention resides in the method of obtaining repeated Vcrossings by means of retarding fields and application thereof in such manner that necessary spacial and phase focusing conditions arefulfilled satisfactorily. I

, ings and referring initially to Figs. 1 and 2, an input Still further objects of the invention will appear to those skilled in the art to which the invention appertains, as the description proceeds, both by direct recitation thereof and by implication from the context.

Referring to the accompanying drawings, in which like numerals of reference indicate similar parts throughout the several views:

Fig. l is a longitudinal sectional view of. a resnatron embodying my invention;

Fig. 2 is a cross-sectional view at a plane intermediate the length of and transversely through the cathode; and

Fig. 3 is a partially diagrammatic View of the structure of Figs. l and 2 and showing circuit connections and indicating electron paths in operation.

In the specific embodiment of the invention, arbitrarily selected for illustrative purposes, the structural details are given by way of example and are not to be understood as limitations to the broader concept admitting substitutions of adjuncts thereto.

Describing the particular resnatron shown in said drawcavity l0 of cylindrical symmetry is provided, said cavity being evacuated and constructed to constitute a resonator. Within the input cavity resonator 1) is a cathode ift, also of over-all symmetrical configuration coaxial to and adjacent the cylindrical wall of resonator liti. An annular series'of openings 12 for electro-ns is provided in the cylindrical wall of the resonator directly opposite or at the level of said cathode, said wall and openings functioning as -a control grid. Outside of and encircling, but spaced from, the cylindrical wall of the input cavity resonator, both above and below as well as opposite said annular series of control grid openings, is a hollow tun able output resonator i3 coaxial with said input resonator. The middle part of the outer peripheral wall of this output resonator is reentrant toward the inner peripheral wall thereof in the region surrounding the control grid and said walls thereat are providedwith coaxial grids 14, 15 separated by a small radial distance from each other thereby providing an annular constrictionor gap 16 between the grid portions of said output resonator. For identifying purposes hereinafter, the grid in the inner or smaller peripheral wall of the output' resonator will be designated the inner accelerator grid ld, and the one in the reentrant portion of the outer peripheral Wall `of the output resonator will be designated the outer accelerator grid 15. These accelerator grids substantially ccntine the portion of the electric field of the output resonator existing in the gap i6 and function for further benecial purposes which will appear hereinafter. The space between control grid i: and accelerator grid 14 may con* veniently be referred to as gap 16a between the reso` nators.

Repeller electrodes are provided coaxial to and at opposite sides of the pair of accelerator grids described above. One repeller electrode, namely the inner one 17, is located between the said inner accelerator grid 14 and the cylindrical wall ofthe input resonator it), whereas the outer repeller electrode 18 is within the reentrant portion of output resonator i3 in proximity to outer accelerator grid 15. The electrons emitted radially outward from cathode l1, while having an initial course toward said repeller electrode 18 and coming to close proximity thereto, are deflected therefrom and ultimately come to rest on one or the other of said accelerator grids i4, l5, as will be explained subsequently herein.

The electron path from the cathode toward the outer repeller electrode i8 is conned from spreading, after passing through the openings i2 of the inner resonator, by entry into and travel through radially disposed flues 19, one for each said opening 12, and of approximately the same size'and configuration as said openings 12.

Said lines are formed in and extend radially through preferably metallic flat rings 21B and 20 which are separated by a distance in an axial direction which somewhat exceeds the height of each said opening 12, the peripheral space between said rings 20 and 2d being subdivided by spacers 19'. Said rings 20 and 20 have their inner periphery close to the cylindrical wall of the inner resonator, but out of contact therefrom so as to avoid electrical connection therewith. The outer periphery of said rings 2t) and 20' are connected to and may conveniently be made as a part of the inner accelerator grid 14 and thereby constitutes a shield and guides for the electrons in their initial radial paths through said inner accelerator grids 14, 15 so the electrons may proceed through outer accelerator grid 15 toward and into proximity to the outer repeller electrode 18. Both said accelerator grids therefore preferably have openings therethrough the approximate size of and in registration with the flues 19.

The repeller electrode 18 is directly opposite the periphery of the shielded fiues and ring and in axial direction extends both ways from the location of said rings. At that part of said repeller electrode 18 directly opposite the annular series of flues 19, there is provided an annular electron deliector 21, here shown as a rib on the inner periphery of and medially between the edges of said electrode and in cross-section triangular, thereby presenting a knife edge toward the stream of electrons advancing toward it. However, instead of the triangular cross-section and knife edge, any other desired protrusion on the retiector electrode toward the shielded electron path may be employed. The function and effect of this deflector 21 is to introduce an electric field with axial component from the repeller electrode that will apply a small velocity component to the electrons perpendicular to the advancing direction of the electrons from the cathode and thereby reflect the electrons at other than 180 from the angle of approach. Simply expressed, the electrons are fanned out when reiiected, and characteristic paths of electrons are indicated by dotted lines 22 in Fig. 3. lt may now be called to attention that in the initial or forward path of electron travel, the rings and 20 shield the electrons from any substantial influence of the electric field of the inner repeller 17 located between the inner resonator cylindrical wall and inner accelerator grid 14.

As indicated in Fig. 3, the electrons approaching outer repeller 18 are reliected and deiiected in proximity thereto, and, being fanned out, pass through outer accelerator grid 15 into gap 16 and then through inner accelerator grid 14 towards inner repeller 17 from which they are again reflected towards gap 16 and so on. The electrons accordingly are subjected to the electric fields between the two repellers and the radio frequency field between the two accelerator grids and as this latter is alternately reversed in polarity resultant from oscillation characteristics of the outer resonator and the p-th of electrons zigzags through the pair of accelerator grids, the electrons can be made to give energy to the resonator gap 16 each time they traverse it.

While the inventive concept may be incorporated in various assemblies, one which provides fer timin,o the resonators, cooling of elements, ready assembly and other features of beneficial electrical and mechanical nature, is illustrated in detail. in conjunction with parts above described, the inner or input resonator is shown as provided with a fixed closure or upper end Wall 23 in proximity and parallelism to a top head 24 for the outer or output resonator. Said top header has a diameter greater than the output resonator and is sealed therebeyond to an envelope or casing wall 25 which surrounds the output resonator in spaced relation therefrom and coaxially therewith. The seal includes an insulating ring 26 so the header and casing may be at different potentials. Beneath the output resonator, spaced therefrom, is an under header 27 integral with the casing wall 25 and provided with an insulating seal 28 to the outer periphery of the inner or input resonator 10 which projects through and below said under header 27 and seal 28. It is at this lower projecting end of the wall of the input resonator that appropriate rigid mounts for the cathode are carried together with means for duid cooling and adjustable control means for tuning the input resonator, all being located coaxially to the resonator.

As shown, the bottom of the input resonator wall has a reducing ring 29 attached vacuum-tight thereto, and depending from the inner circumference of said ring is a cylindrical insulating seal 30 below which is carried a peripherally exposed intermediate ring 31 and therebelow another cylindrical insulating seal 32 for a bottom header 33. Projecting upwardly from intermediate ring 31 is a tubular conductor 34 extending to the level of the lower ends of the cathode strands and carrying a ring 35 thereat to which all of rsaid strands ure secured. Within and projecting from both ends of tubular conductor 34 is an inner tubular `conductor 36 the lower end of which is made fast in bottom header 33. Next to the upper end of said inner conductor 36 is another ring 37 overlying the top ring 35 of the outer conductor in spaced relation thereto and to this overlying ring 37 are secured-the upper ends of the filament or cathode strands, thus providing fan electrical circuit from one tubular conductor to the other with said cathode strands in series therewith. It will be seen that individual supply voltages can be given, by virtue of the described insulating seals, to the ends of the cathode heater 35, 37 to the inner resonator cylinder 1t), the accelerator grids 14, 15, and to the repellers 17, 18.

inside of inner conductor 36 is a baille tube 38 also carried by the bottom header 33 but not extending quite to the top of said conductor tube 36 so arranged to provide an annular conduit space between said tube for ow of a cooling fluid from end to end thereof and over the tcp of the baille tube. Inside the batiie tube, spaced radially therefrom to also provide for the iiow of the cooling fluid, is a tunnel tube 39 which also extends from bottom header 33 and projects above the end of the bafe and inner conductor tubes 38 and 36 respectively. A closure cap 4t) is sealed to both said inner conductor tube 36 and tunnel tube 39 above the end of blatiie tube 3S for preventing loss of vacuum thereat or escape of cooling fluid from the conduit space into the resonator. Aporopriate in-flow and out-flow pipes 41, 41a are provided to the bottom header 33 and lower ends of the conduit spaces on opposite sides of the baffle tube.

Above the ends of the several tubes above described and within the inner resonator 16 is a transverse movable plate 42 having an under shoulder 43 to which is secured, vacuum-tight, the upper periphery of a bellows 44 the lower end of which is made vacuum-tight to said closure cap 4i). laid plate has a downwardly extending internally threaded stem 45 which receives a threaded upper end of a rod 46 vhich is rotatable for moving said plate up and down 'fially of the resonator. The rod is kept from longitudin^l movement by a flange 47 thereon seating within cap "l and retained on its seat by a retaining nut 4S in the cap -hove said shoulder and flange. Said rod extends down- `V"ily through tunnel tube 39 and projects below bottom "te dir 33 where it is provided with a suitable knob or other control means 49 available to the operator. Manipuiation of the knob moves the said plate closer to or further from the upper end wall 23 of the resonator thereby changing the capacitance and tuning the resonator as desired. It may also be here noted that the conductor tubes are preferably equipped with appropriate choke collars Sti, 51 and 52 for preventing the high frequency current from dissipation to the exterior between the conductor tubes 34 and 36 and between conductor tube 34 and resonator 1t), although each pair of tubes has to have an insulating means between them.

Qooling of the .accelerator grids is yobtained in the v55' present showing by constructing the same a's hollow honeycombs communicating at top and bottom marginal ends with hollow-wall spaces 53 in the walls of outer or output resonator 13. Suitable in-flow and out-flow pipes 54, 55 respectively are introduced through top header 24 to said spaces 53 for the cooling fluid.

Tuning of the out-put resonator may be elected by suitable means for varying its effective volume, such as by an annulus 56 in the upper region of the resonator. The peripheral edges of this annulus are shown making resilient contact with the fixed walls of the resonator as one means of obtaining electrical continuity thereat. The annulus may be supported at intervals by rods 57 projecting through the header and made vacuum-tight and adjustable by interposed bellows 58.

Mounting of the inner repeller 17 is obtained by seating the lower end in the inner rim of the intermediate or under header 27 with a solder or other permanent joint. Mounting of the outer repeller 18 is by means of a centrally cut-out disc 59transverse to the axis 0f the repeller and secured medially between the ends of said repeller. This disc 59 extends outwardly to and included between butt flanges 6l! forming a sealed joint in the length of outer casing 25. By virtue of electrical isolation obtained by in- :ulating seals 26 and 2S, said casing with the attached repellers are at a common potential in use. Inner resonator 10 is isolated by the seals 28 and 30 and outer resonator 13 is isolated by seal 26, it being remembered that the control grid is part of the inner resonator. These several isolation cf parts of the device keeps the potentials thereof separate. input and output loops 61, v62 respectively -e sho n for h: input and output resonators.

For simplicity of explanation of operation, reference may be had to Fig. 3 wherein a density modulated beam is accelerated toward a liue opening 19. The density modulation is shown performed in a manner typical of resnatrons, namely, by the biased grid of the input cavity l0. The modulated beam 22, having arrived at a potential equal to that of the screen or accelerator grids 14, 15 traverses the same and the resonator gap 16 and enters the decelerating field of repeller 18 which reects it back through grids 14 and 15 and intervening gap 16. The retarding field, by virtue of deector 21 gives to the electrons a small Velocity, component perpendicular to the initial direction as a result of which the beam does not revert into itself. After traversing the resonator gap in this first reliection and deflection, and passing grid 14, the beam enters the retarding field of repeller 17 on the other side, and is again reliected to pass back through the grids and gap into the opposite retarding lield of repeller 1S, and so on, and since the electrons essent-ially maintain the small perpendicular velocity component, they will describe an oscillating path as shown in Fig. 3. At each crossing the beam loses la certain amount of energy, the penetration into the retarding field becomes progressively smaller, and the electrons are finally caught by the grid system comprising grids 14 and 15. v

After the electrons have spent their kinetic energy, they are preferably caught by the screen grids 14, 15 which are on the same direct current potential. This can be accomplished by forming the electrode system so that the electrons will, after going through the prescribed number of cycies, leave the foraminous region and arrive at the solid boundary of the grids. Another more eiicient arrangement consists in providing progressively narrowing sizes of grid openings in the vicinity of approach to the lateral extremities of the grids. The grids serve both as eld boundaries and as terminals for the electron trajectories. The probability of capture of slow electrons is much higher than for fast ones, so electrons which, because of phrase defocusing, still retain at the marginal position of the grid an appreciable fraction of their kinetic energy are given additional chances to contribute to the radio frequency power by continuance of grid openings to the greatest possible extent.

The electrons must fulfill the resonance condition of spending about half a period (T/2) of oscillation between successive crossings of the middle of the cavity gap. It can be seen that an electron which crosses a gap of width d with a speed v1 will, in effecting a crossing half-way of the gap and in the retarding field of the repeller which gives it the negative acceleration a, and then coming back halfway through the gap, consume time t according to the following formula This shows that the resonance condition cannot be strictly fulfilled during the entire time the electron is oscillating, inasmuch as its velocity is varying from a maximal value to nearly zero. It can be shown, however, that for a velocity vo of such value that the electron spends equal time in retarding field as in the gap, changes in velocity from vo produce a minimum effect on the return time between successive crossings. In fact', if vo is chosen to be three-quarters of the initial velocity due to the screen grid voltage, the electron will decelerate to half of its velocity, that is, it will have given of its energy to the field before the detuning reaches more than 2.5 to 5% as maximum deviation per cycle. An electron, therefore, which goes through five cycle with 75% eiiiciency will have an average detuning effect in the order of 5 (remembering that the phase of the radio frequency field adjusts itself to the electron current). If the design parameters are correctly adjusted, therefore, the detuning from the resonance condition is negligible. Considering that time t is given by the operating frequency, there are three adjustable parameters, namely, the tuned velocity vo, gap width d, and the acceleration a due to the repeller voltage. The value vo is given by the requirement that it correspond to about nine-sixteenths of the screen voltage. The width d is then given by the condition of equal times, by the formula Finally, the repelling iield is given from the condition of resonance following the formula of The preferred method of wide band modulation consists in swinging the repeller voltage around a fixed bias. It is also possible in principle to modulate at the input stage, but only a system like the travelling wave helix, to be used in this case for density bunching, has suicient band width' for such an arrangement. The modulation of the repeller voltage can be operated either with a bias which is negative or slightly positive with respect to the direct current cathode potential or secondly, with appreciably positive bias with respect to the cathode. In the irst instance of a bias negative or slightly positive, the modulation consists essentially in varying the transit tim-e, phase and number of useful cycles of the electrons. The electrons will, under all conditions, be finally absorbed by the screen grids, and the modulation driving power may be Very small. In the second instance, namely, with appreciably positive bias, the modulation is largely of the pure adsorption type inasmuch as the electrons, to a degree depending on the instantaneous value of the repeller voltage swing, are partly able to reach the repeller to be collected there. This absorption modulation makes greater demands on the driving power of the modulator, but might be of advantage in a very low loaded Q operation where it minimizes an otherwise-occurring contribution of frequency modulation. A third possibility may also be mentioned, namely, modulation by Varying the screen grid voltage.

According to the foregoing, a device is provided having r an extremely large band width of relatively high eiiiciency and power kkcapabilities in which a density modulated beam repeatedly crosses the gap of an input cavity resonator. Operationof theY device utilizes retarding fields during the passage of the beam in the repeated crossings of the gapand in such manner that the necessary spacial and phaseA focusing conditions are fulfilled. The transit or absorption modulation obtained in the output cavity is accomplished'with negligible, or at most very low power. The structure is of a character conductive to relative independence of generator operation with respect to load changes in the operating region.

I claim:

1. Aresnatron comprising an input resonator and an output resonator, said resonators having a gap therebetween and said gap having an opening into each resonator, said gap extending in a direction substantially perpendicular to the said opening, a cathode opposed to said openingrfor emission of electrons to travel on a forward patrl through said opening, and reflective means having a medialrprojection opposed to said cathode beyond said opening and proximate to said gap for directing and conducting the electrons away from said opening in laterally opposite directions from said projection on average paths in said gap substantiallyperpendicular to said forward path of emission of said electrons through said opening.

2. Avresnatron comprising an input resonator and an output resonator, said resonators having a gap therebetween and an opening into each resonator, a cathode opposed to said opening between the resonators, grids perpendicular to said opening deiining the gap spacing, one of said grids being closer than the other grid to the cathode and constituting a control grid, a iiue extending from said other grid toward the control grid and cathode in a direction across said gap, and a reflector having deliecting means opposed to said cathode and aligned medially of said flue.

3. A resnatron comprising an input resonator and an output resonator, said resonators vhaving a gap therebetween and an opening into each resonator, a cathode opposed to said opening between the resonators, grids perpendicular to said opening defining the gap spacing, one of said grids being closer than the other grid to the cathode and constituting a control grid, a flue extending from said other grid toward the control grid and cathode in a direction across said gap, and-a reflector having deecting means opposed to said cathode and aligned medially of said ue and insulating means electrically isolating the cathode, control grid, gap-delinnig grids and reliector from each other.

4. A resnatron comprising an input resonator and an output resonator, said resonators having a gap therebetween and an opening into each resonator, a cathode opposed to said opening between the resonators, grids perpendicular to said-opening into said input cavity defining the gap spacing of said input cavity, a pair of grids perpendicular to said opening into said output cavtiy defining thegap spacing of. said output cavity, said pair of grids each having a series ofvopenings spaced beyond and in a perpendicular direction to said opening into said output cavity, a pair of repelling electrodes spaced from said pair ofl grids insaid output cavity, line-forming means extendingifrom said output cavityl toward said cathode defining the'- width of said opening between said resonators, and insulating means electrically isolating the cathode, input cavity grid, gap delining grids of the output cavity, and repelling electrodes from each other. v

5. A resnatron comprising an input resonator and an output resonator, a cathode consisting of a series of elements in said input cavity, a control grid in said input cavity having a series of openings in opposition to said cathode elements, a pairof accelerator grids in said output cavity having a series of openings aligned in opposition to said openings of the control grid, said pair of accelerator grids having in addition a series of alignments of openings perpendicular to the alignment of said series of control grid openings, a pair of reflecting electrodes in juxtaposition to said pair of accelerator grids, shielding fine means extending from one of the said pair of accelerator grids through one of said pair of repeller electrodes to proximity of said control grid, a projection on the profile of one of the said pair of repeller electrodes, insulating means connecting and electrically isolating the cathode, control grid, accelerator grids vand reflector electrodes, and cooling means for said grids and cathode.

6. A resnatron comprising an input cavity resonator and an output cavity resonator, a cathode, a control grid having openings, two accelerator grids having a network of openings in spaced relationship to openings in said control grid, two reiiecting electrodes in spaced relationship to said accelerator grids, a projecting edge pointed towards the cathode on one of said repelier electrodes, and shielding means in the space between the openings of said control grid and one of said accelerator grids.

7. A resnatron comprising an input cavity resonator and an Output cavity resonator, a cathode and control grid opposite each other bounding said input cavity resonator, a pair of accelerator grids opposite each other bounding said output cavity resonator, two reflecting electrodes respectively on opposite sides of said pair of grids, said pair of grids having a network of openings of predetermined sizes and positions, one of said reflecting electrodes having a projecting edge opposite the cathode and having angularity to the direction of an electron beam emitted from the cathode toward said edge such that said beam on passing through and being controlled by the control grid and through and accelerated by the accelerator grids will be reflected at an angle smaller than from said reiiector having the projecting edge and will successively and repeatedly penetrate the gap between said accelerator grids and traverse repeatedly the openings of said network and be reliected repeatedly by said refleeting electrodes.

References Cited in the tile of this patent UNITED STATES PATENTS 1,590,413 Bol et al. June 29, 1926 2,167,201 Dallenbach July 25, 1939 2,190,511 Cage Feb. 13, 1940 2,190,515 Hahn Feb` 13, 1940 2,405,611 Samuel Aug. 13, 1946 2,468,152 Woodyard Apr. 26, 1949 2,482,769 Harrison Sept. 27, 1949 2,485,400 McArthur Oct. 18, 1949 2,581,408 Hamilton Jan. 8, 1952 

